Impact tools

ABSTRACT

Hydraulic impact tools are described which develop percussive forces for rock drilling and other repetitive high force applications. A self-excited oscillator is disclosed which includes a hammer and a valve coaxial with and actuated by the hammer for controlling the flow of pressurized hydraulic fluid. The hammer is accelerated away from an impact position to store energy in an energy storage system. The stored energy in the system is eventually returned to the hammer to drive it at increasing velocity back to its impact position. Accumulators forming part of the oscillator are closely coupled to the hammer by way of hydraulic galleries or channels and operate in concert with the hammer to provide energy storage characteristics for oscillator operation and to reduce fluctuations in the flow of hydraulic fluid and to provide for efficient operation of the oscillator.

United States Patent Bouyoucos Oct. 14, 1975 IMPACT TOOLS [75] Inventor: John V. Bouyoucos, Brighton N.Y. [57] ABSTRACT [73] Assignee: Hydroacoustics, Inc., Rochester, Hydraulic impact tools are described which develop N.Y. percussive forces for rock drilling and other repetitive high force applications. A self-excited oscillator is dis- [22] 1974 closed which includes a hammer and a valve coaxial [21] App]. No.: 463,626 with and actuated by the hammer for controlling the flow of pressurized hydraulic fluid. The hammer is ac- 52 US. Cl 91/321; 92/134 celerflted y from an pact plohsition to store e 51 Int. c1. FOlB 7/18; F01B 31/00 ergy Storage System B energy [58] Field of Search 91/321 276 92/134 the system IS eventually returned to the hammer to drive it at increasing velocity back to its impact position. Accumulators forming part of the oscillator are [56]. References Clted closely coupled to the hammer by way of hydraulic UNITED STATES PATENTS galleries or channels and operate in concert with the 3,4I 1,592 11/1968 Montabert 91/321 hammer to provide energy storage characteristics for g gli f oscillator operation and to reduce fluctuations in the i i flow of hydraulic fluid and to provide for efficient op- 3,796 ,050 3/1974 FISk 92/134 eration of the Oscillator.

Primary ExaminerPaul E. Maslousky Claims, 15 Drawing Fi Attorney, Agent, or Firm-Martin Lukacher If! I IGLGH I68 "I70 US. atei Oct. 14, 1975 Sheet 1 of 8 US. atem 0m. 14, 1975 Sheet 2 0f 8 3,911,789

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US. atent 001;. 14, 1975 Sheet 3 of 8 3,911,789

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US. Patent Oct. 14, 1975 Sheet 4 of 8 3,911,789

US. Patent Oct. 14, 1975 Sheet 5 of8 3,911,789

V|N DRIVE CAVITY (94) VNETTHROUGH PoRTulz) v THROUGH GALLERY (I08) V AS SEEN BY RETURN CHANNEL (I46) FIGS.

US. Patent 0a. 14, 1975 Sheet 6 of 8 3,911,789

v TO DRIVE CAVITY (33o) VNETTHROUGH PORT (356) VOUTAS SEEN BY RETURN CHANNEL (37o) v TO SECOND CAVITY (332) US. Patent Oct. 14, 1975 Sh6et 7 of 8 3,911,789

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US. Patent 0m. 14, 1975 Sheet 8 of 8 3,911,789

IMPACT TOOLS The present invention relates to impact tools and particularly to hydraulically operated impact tools which generate percussive energy. This invention is related to the invention described in US. Pat. application Ser. No. 285,240, filed in the United States Patent Office in the name of John V. Bouyoucos, on Aug. 31, 1972, and is an improvement thereon, and also to a patent application filed in the United States Patent Office in the name of John V. Bouyoucos and Roger L. Selsam simultaneously with this application Ser. No. 463,625, all of which applications having a common assignee.

This invention is especially suitable for use in rock drilling, pile driving, demolition and rock ripping work, in construction, mining and the like fields. The invention is particularly applicable for providing small size, high efficiency rock drills for use in mining and construction. The invention is also applicable to apparatus for generating high blow energies at high repetition rates (i.e., high power levels) and with high efficiency, thereby to obtain improved performance in any application where percussive energy at high power levels is needed.

The related application, Ser. No. 285,240, describes tools for generating percussive forces at a load in which a hammer provides a mass which is part of a mass spring oscillator system. The motion of the mass is coupled to a valving mechanism in a hydraulic fluid-filled cavity, switching the pressure of the hydraulic fluid in that cavity abruptly between return and supply pressures to obtain driving forces which accelerate the mass with respect to the spring system. The energy of the accelerated mass is transferred to the spring system which, when the valve mechanism subsequently switches the pressure in the cavity to remove the accelerating force, decelerates the mass to zero velocity and then drives the mass with increasing acceleration in the opposite direction towards the load. Percussive energy is generated upon impact of the mass with the load. The spring system is provided by a'further hydraulic fluid filled cavity, the dynamic spring rate or stiffness of which may be selected to tailor the motion of the hammer mass and the energy transfer characteristics of the tool. The spring cavity may, for example, be divided into a pressurized gas filled region and a hydraulic fluid filled region; the pressurized gas operating to reduce the dynamic spring rate or stiffness of the spring portion of the system towards zero so as to provide a constant force upon the hammer and to obtain a relaxation oscillation cycle. This oscillation cycle is especially useful in generating high percussive forces in small tools as are frequently desired in rock drilling.

The desirable energy storage and spring characteristics provided in accordance with the invention of the above identified related application Ser. No. 285,240 can be obtained while at the same time minimizing flow fluctuations and providing open flow channels and large peripheral porting lengths for the fluid flow through the switched cavity in a manner to improve the efficiency as well as to reduce the size and simplify construction of impact tools also embodying the present invention. 5

It is therefore an object of the present invention to provide improved impact tools.

It is another object of the present invention to provide an improved hydroacoustic oscillator.

It is a still further object of the present invention to provide improved hydraulically operated percussive tools capable of providing high energy per blow even at high impact rates which may be configured in a manner to reduce their size and weight.

It is a still further object of the present invention to provide improved hydraulically operated percussive tools which are efficient in operation.

It is a still further object of the present invention to provide improved hydraulically operated percussive tools in which the fluctuations of flow of the hydraulic fluid are minimized and in which the efficiency of operation and performance is also improved.

Briefly described an impact tool embodying the invention includes a housing in which a piston which provides a hammer can oscillate longitudinally in a direction toward or away from a position where it may impact a load. The piston defines at least a first and a second cavity in the housing. The volume of these cavities vary in opposite senses with the movement of the piston in the same direction. The area of the face of the piston which varies the volume of the first cavity when it moves is larger than the area of the moving face of the piston which varies the volume of the second cavity. The first cavity has a valve mechanism associated therewith which includes a valve element moved by the piston which alternately opens and closes supply and discharge ports into the first cavity for establishing alternating fluid pressures upon the piston at a frequency determined in part by the mass of the piston and the pressure and compliance of the fluid presented to the mass in the cavities. In order to provide a spring which stores the energy developed when the piston is accelerated in response to the fluid pressure in said cavities, a third cavity is provided which is in communication with the second cavity. The third cavity is also associated with energy storage means which provides the spring portion of the system and may include an accumulator containing a region of compressible gas which affords a pressure release. This third cavity communicates not only with the second cavity, but also with the first cavity, through the supply port, and with the supply of the pressurized hydraulic fluid. Accordingly, the third cavity maintains substantially constant pressure in the second cavity and in the first cavity when the supply port is open, and simultaneously stores energy which is hydraulically coupled thereto from one of the first and second cavities. When the supply port to the first cavity is open the third cavity and its communicating channels provide a direct path for the circulation of hydraulic fluid between the first and second cavities due to the difference in areas presented by the faces of the piston presented to the two cavities, thereby to reduce the net fluid volume displacement required of the third cavity and its associated accumulator. The accumulator capacity requirement is thereby reduced. The third cavity may conveniently be mounted in a laterally displaced position from the piston, thus enabling an impact tool design which is reduced in size.

The piston mass oscillates in a self-excited mode at a frequency determined by the mechanical and acoustical characteristics of the spring, mass and valve mechanism elements associated therewith. This self-excited oscillator is therefore a hydroacoustic oscillator.

The foregoing and other and additional objects, advantages and features of this invention will become more apparent from a reading of the following description in connection with the accompanying drawings in which:

FIG. 1 is a plan view of a hydraulically operated impact tool embodying the invention, the view being broken away to illustrate the internal construction of the tool;

FIG. 2 is a top end view of the tool shown in FIG. 1;

FIGS. 3A and 3B are fragmentary sectional views of the tool shown in FIG. 1, the views being taken along the lines 3A3A and 3B3B in FIG. 1;

FIGS. 4, 5, 6 and 7 are fragmentary views of the tool shown in FIG. 1 each in a different position during the cycle of oscillation; the various portions of the cycle depicted in each of the views being shown in curves immediately above each view;

FIG. 8 is a fragmentary plan view illustrating another hydraulically operated impact tool in accordance with this invention and also embodying improvements provided by the invention of the above mentioned application Ser. No. 463,625 of John V. Bouyoucos and Roger L. Selsam.

. FIG. 9 is a series of curves illustrating the displacement and flow characteristics of the tools illustrated in FIGS. 1-7, and 11.

FIG. 10 is a series of curves illustrating the displacement and flow characteristics of the tool illustrated in FIG. 8; and

FIGS. ll, 12, 13 and 14 are transverse sectional views schematically illustrating tools in accordance with different embodiments of the invention.

Referring more particularly to FIGS. 1, 2 and 3A and B. There is shown an impact tool especially adapted for generating percussive forces for drilling blast holes as in mining, construction, and quarrying work. The tool has a housing 10 in which a piston 12 can execute oscillatory motion along the longitudinal axis of the housing. The piston 12 serves as a hammer which impacts a shank 14. The shank 14 is part of an anvil system which transmits force pulses created by the impact of the lower end of the piston 12 thereon to a load which may consist of a drill steel and rock bit engaged with a rock interface. A chuck assembly 16 holds the shank 14 for rotation by means of a hydraulic motor 18 which is coupled by gearing 20 to the chuck 16. Hydraulic fluid for operating the motor 18 is supplied and discharged through supply and return lines 22 and 24 (FIG. 2). Reference may be had to US. Pat. No. 3,640,351 issued Feb. 8, 1972 and also to the patents cited therein for further information respecting the design of the shank 14 and chuck 16.

The above referenced patent also discusses the use of the passages such as the bores 26 and 28 in the piston 12 and shank 14 in which a tube 30 is located for the passage of cleansingfluid, suitably air or water, for flushing and cleaning the holes drilled by the tool. In order to prevent the reverse circulation of the cleansing fluid through the hole 26 while allowing the shank 14 to move longitudinally and to rotate, U-cup seals 32 are located around the tube 30 in the shank 14. The upper end of the tube 30 may be flanged and sealed in the upper end cap 34 of the housing 10 by means of a hose coupling 36 which compresses a washer 38 to seal the upper end of the tube 30.

The housing 10 is made up of a central member 40, the upper end cap 34 and lower end 42 which may be assembled together by suitable bolts and screw arrangements; only the bolts 46 in the upper end cap 34 being shown to simplify the illustration. Internal of the central member is a sleeve 48 which defines a central housing bore 50 in which the piston 12 oscillates. 0 rings or other suitabe seals 52 are provided between the interfaces of the sleeve 48 and the central housing member 40 as well as elsewhere between the interfaces of the other housing members and parts to provide fluid seals. The seals between interfaces which slide or rotate with respect to each other are preferably of the U-cup type.

Attached to the central housing member 40 and laterally offset with respect to the axis of the housing are a supply accumulator 54 and a return or discharge accumulator 56.

It will be understood that the hydraulic fluid is pressurized by a suitable pump having a supply and a return which may be connected by hoses or other lines to the tool in a closed loop circuit. In the event an open loop circuit is used fluid may be discharged, as to a sump, instead of going to the return side of the pump. Thus terms discharge and return should be taken as comprehending flow to the pump return side or otherwise to discharge.

The accumulators are shown disposed immediately above the hydraulic rotation motor 18. They may also be located in other locations as illustrated in FIGS. 8 and ll-l4. It is a feature of the invention to facilitate the location of the accumulators 54 and 56 in a manner as shown in order to reduce the envelope (size) and particularly the length of the tool. The accumulators themselves have two sections 60 and 62 which are clamped together as by bolts 66 which also clamp a flexible diaphragm 68 therebetween. Holes 76 in the front wall of the section 60 provide a channel for the entry of fluid into the accumulator and retainment of the diaphragm by the front wall. The diaphragm separates the interior of the accumulator into two regions 70 and 72. The outer region 72 may be filled with a compressible fluid (e.g., a gas such as air) through a valve 74. The inner region 70 is filled with hydraulic fluid during operation of the tool which fluid enters through the array of holes 76 in the inner wall of the accumulator part 60. When the accumulators are filled with hydraulic fluid and air at operating pressure levels, the diaphragm 68 assumes the position shown in dashed lines in the drawing. The accumulators act as energy storage means, as will be explained more fully hereinafter.

The lower end 42 of the housing and the interior of the upper end cap 34 are both vented to the atmosphere. An opening 93 in the end cap vents the region 92 and minimizes the compression of the air therein when the hammer 12 moves upwardly away from the impact point.

The piston 12 has an upper section 78 adjacent to which is a center section 80 which is of a diameter larger than the upper section 78 so as to form a step 82 therebetween. The piston 12 also has a lower section 84. The lower section 84 has a diameter smaller than the center section 80 and defines another area which is presented by a step which, together with the step 82, defines the differential area of the piston. The step 90 may suitably have twice the area of the step 82. Other area ratios may be employed to achieve different force balance conditions. While the differential area is shown as provided by the steps 82 and 90, it may be presented by other surfaces which may be made up of a plurality of steps or may be of curved shape, such areas or surfaces nevertheless have forces thereon the net total of which depend upon the pressure levels and the net projected areas in a plane normal to the axis of piston motion, such net projected areas being referred to generally by the term faces herein.

The lower section of the piston 12 is formed with a ring 86 and another ring 88 which is spaced therefrom, which rings operate the valve mechanism 85 and will be described in detail hereinafter.

The end faces of center section 80 of the piston 12 define two variable volume cavities 94 and 96 within the bore 50. The cavity 94 is a first or drive cavity, the volume of which increases by virtue of the movement of the face defined by the step 90 in a direction away from the impact position at the shank 14, while the second or upper cavity 96 decreases in volume for movement in the same direction due to the movement of the face defined by the step 82. The upper cavity 96 is effectively sealed by the U-cup seals 98 around the section 78 of the piston 12. These seals 98 may be located in an upper part 99 of the sleeve 48; the part 99 facilitating assembly of the piston in the housing 10. The lower or drive cavity 94 is sealed by U-cup seals 100 disposed in the sleeve 48, around the lower section 84 of the piston 12. The sleeve 48 and the outer member 40 of the housing also form a third cavity 106 which is in the form of a cylindrical gallery encompassing the bore 50 and laterally displaced therefrom.

The valve mechanism 85 is associated with the drive cavity 94. Supply and return or discharge ports 102 and 104 respectively, are provided by peripheral internal grooves 105 and 107 in the sleeve 48. These grooves are in communication with the galleries 106 and 108 through lateral passages 109 which occupy a substantial portion of the periphery of the sleeve 48 (see FIG. 3B) to present a low inertance to the flow through the ports 102 and 104. The gallery 106 extends between the supply port 102 and an opening 110 to the upper cavity 96 and thus communicates the upper cavity 96 and the drive cavity 94 when the supply port 102 is open. The holes 76 in the inner part 60 of the supply accumulator 54 also provide an essentially unrestricted channel which communicates directly with the gallery 106 and therefore via the gallery with the upper cavity 96 and drive cavity 94. The supply accumulator holes 76 are disposed opposite to an opening 112 in the housing section 40 which is directly adjacent the opening 110 and extends between these holes and the gallery 106. A channel 114 connects the opening 112 to a coupling 116 through which the supply line from a source of pressurized hydraulic fluid, say a hydraulic pump which supplies fluid pressures in the range of 2000 to 3000 psi, may be connected.

The return accumulator 56 also has the holes 76 which provide the entry channel, in the front wall of its inner part 60, in direct communication with the lower gallery 108 such that the accumulator 56 is connected to the drive cavity 94 when the return port 104 is open. The return line for the hydraulic pump is connected to a coupling 118 to which a return line 120 extends downwardly into the gallery 108 (seev FIG. 2), the return line 120 being disposed behind the supply line 114.

Returning to the valve mechanism, in addition to the ports 102 and 104, the valve mechanism includes a valve element 122 in the form of a hollow cylindrical member or sleeve which is coaxial to lower section 84 of the piston which is located between the rings 86 and 88 and which is slidably mounted with respect to the bore 50. The valve element is shown having longitudinal dimension essentially equal to the distance between the outer edges 123 and 125 of the grooves providing the supply and return ports 102 and 104. The inner periphery of the valve element is also formed with longitudinally extending slots 124, (cusp-shaped in crosssection as shown in FIG. 3) which provide an unrestricted passage for the hydraulic fluid therethrough. The lower edge of the ring 86 engages the upper end of the valve element 122 as the piston moves down so as to open the supply port 102 and close the return port 104. The ring 88 engages the lower end of the valve element 122 as the piston moves up so as to open the return port 104 and close the supply port 102. The upper and lower ends of the valve element are preferably provided with damping means such as steps which effectively form dash pots with the rings as more fully described in the above referenced Bouyoucos application Ser. No. 285,240.

The large diameter (equal to the maximum piston diameter) of the valve element 122 and its coaxial arrangement with respect to the large area galleries 106 and 108 reduces inertance in the dynamic flow path and increases power conversion efficiency. This feature is especially advantageous at high output power levels (i.e., high flows) where inertance becomes even more significant. The large diameter valve enables the pressure drop across the ports to be maintained at a low value until the last instant of valve closure, thereby reducing hydraulic power losses and providing high efficiency.

The operation of the impact tool as shown in FIGS. 1, 2 and 3, will be more apparent from FIGS. 4 through 7 which illustrate the piston 12 in different positions during its cycle of oscillation and from curves (a) through (d) in FIG. 9. FIG. 4 shows the piston 12 at the beginning of thecycle of oscillation with the piston in its displaced position at impact with the shank 14. This is indicated as time t T The upper ring 86 has moved the valve element 122 so that both the supply port 102 and the return port 104 are momentarily closed. After the piston reaches the impact position, the valve element may move, due to its own inertia, to a position below that shown in FIG. 4 where the supply port is open andv the return port closed. Pressurized fluid is supplied to the drive cavity 94 and accelerating forces are applied to the drive face formed by the step 90. The pressurized fluid is also applied to the upper cavity 96. The piston 12 has its differential area A presented to the pressurized fluid in these cavities 94 and 96; the area of the face formed by the step being larger than the area of the face formed by the step 82. The net force applied to the differential area is therefore in the upward direction and accelerates the piston upwardly. Thesupply accumulator 54 tends to keep the pressure in the drive cavity 94 constant since the compressed gas in the region 72 thereof acts as a pressure release. The piston 12 then moves upwardly a distance X equal to the difference between the distance between the opposing faces of the rings 86 and 88 and the length of the valve element 122. The accelerating forces are applied until the lower ring 88 moves the valve element 122 to the position shown in FIG. 5, immediately after which the valve element closes the supply port 102 and opens the return port 104. This occurs at a time in the cycle T The pressure in the drive cavity 94 is then switched from supply to return and the direction of force on the piston is switched to decelerate the piston motion as shown in FIG. 6. Energy has been transferred during the period from T to T, to the piston mass to give the piston kinetic energy.

After the piston 12 has travelled over a time period t= T T the piston has decelerated to zero velocity and has transferred its kinetic energy to the spring system presented by the hydraulic fluid in the cavity 96 as well as in gallery 106 and in the supply accumulator 54. Inasmuch as the accumulator 54 includes the pressure release region 72 which affords a constant spring force (viz., the dynamic spring rate or stiffness being reduced toward zero) a relaxation oscillator characteristic is obtained as shown in waveform (a) of FIG. 9 and in the waveforms at the tops of FIGS. 4 through 7. The energy introduced by the accelerating forces applied to the piston during the time period T to T, as well as its displacement over that interval, is then transferred back to the piston to drive it downwardly towards impact. As shown in FIG. 7, during the time period t greater than T but less than Tp, T being the impact time at the end of the cycle, the discharge port 104 remains open while the supply port 102 remains closed. Port switching occurs immediately after impact, and the impact reaction force assists the supply pressure in driving the piston upwardly to begin the next cycle of oscillation. The force on the average which is in the upward direction due to the impact event and also in the upward direction during the time interval T is balanced by forces in the downward direction during the time interval from T to Tp. The ratio of the areas presented by the steps 90 and 82 may nominally be 2:1, but may also be adjusted to provide a specific force balanced condition on average. The forces due to the impact events as well as the losses in the system are considered in providing the exact ratio.

The blow energy E applied to the shank 14 at the end of each cyclejs proportional to the potential en ergy possessed by the piston at the top of its stroke at time t T This energy may be expressed by the following equatiom E8 1 (PSAFXP) l) where k, is a constant, P is the supply pressure and Xp is the total piston travel to the top of its trajectory. In the case where the area of the step 90 is twice the area of the step 82, the total piston travel distance to the top of its trajectory is approximately twice the distance travelled over the time interval T to T The total piston travel is then given by:

Xp 2X (2) The frequency, 1",, of oscillation may be derived from the kinetic and potential energy relationships and may be expressed as where k is a constant and Mp is the mass of the piston.

The arrangement of the supply port 102, the opening 110 and the gallery 106 provides a direct path and permits the fluid to flow back and forth (viz. exchange) between the upper cavity 96 and the drive cavity 94, so as with the aid of the supply accumulator 54, to provide the dynamic flow requirements of the tool and to reduce pressure fluctuations in the supply region which might otherwise interfere with the oscillation cycle. Curve (b) of FIG. 9 shows the volume V,-,, transferred to the drive cavity 94 through the supply port 102. This volume transfer occurs during the time interval T to T and is equal to X A over the interval T to T A is the area presented by the step 90 to the drive cavity 94. A,; is the area presented by the step 82 to the upper cavity 96. Volume changes due to the compressibility of the hydraulic fluid and the elasticity of the sleeve 48 and other housing members is neglected for purposes of explanation. Since the total piston travel in the upward direction is X which is twice X,, for this exemplary case, the following relationships respecting the volume displacement V in the drive cavity 94 and the volume displacement V in the upper cavity 96 exist.

van-T.) Van-T.) (s) The net volume supply to both the drive cavity and the upper cavity over the time interval T to T during which interval the port to the drive cavity is open is therefore Xp VNET o( TI TO) VE( i o) 4 and upper cavity through the gallery, during the time interval T T creates less of an instantaneous demand on the supply than would the requirements of the drive cavity alone, and reduces the flow requirement from the accumulator 54. Thus, the accumulator is better able to maintain the supply pressure constant over the entire cycle of oscillation. During the time interval from T to Tp the supply port 102 is closed so that the volume handled by the supply accumulator 54 is the difference between the input volume passing through the .channel 114 and the volume displaced by the area A of the step 82. Over the first portion of this interval (between T and T the area A is expelling fluid from the upper cavity 96 back into the supply accumulator 54. As the piston moves down through its full stroke, during the interval from T to Tp, the upper cavity 96 accepts flow from the accumulator 54 and from the supply in an amount equal to X A which amount is one-half the volume displaced from the drive cavity into the return accumulator 56.

In FIG. 9, the dashed lines represent the average displacement rate. This is also the case in FIG. 10. The displacement curves of FIG. 9 (c) illustrate that when the common channel (gallery 106) interconnects the accumulator 54 and the drive and upper cavities, the fluctuation or ripple in the flow is reduced over the ripple which would exist if the upper cavity 96 was fed from a separate accumulator which would then have to supply the displacement shownin curve (b).

Curve (d) of FIG. 9 shows the volume displacement as seen by the discharge accumulator 56. Over the time interval T to T the discharge or return port 104 is closed, such that the volume does not change. Immediately after time T the port 104 opens, and the piston 12 is continuing its upward trajectory. Flow is therefore backwards through the port 104 and into the drive cavity 94. This flow is supplied by the discharge accumulator 56. From time T to impact at time T, the flow is out of the port 104 and the accumulator accepts a peak volume displacement X A The ripple or fluctuation as seen by the discharge accumulator 56 is greater than the ripple or fluctuations as seen by the supply accumulator and shown in curve (c) of FIG. 9. However, such fluctuations are at the low pressure of the discharge or return side of the tool which can be readily handled by the discharge accumulator. If it is desired to minimize such fluctuation and ripple, an impact tool in accordance with the embodiment of the invention illustrated in FIG. 11 or FIG. 13 may be used. The tool shown in FIG. 8 also minimizes fluctuations or ripple in the discharge accumulator. As will be explained more fully hereinafter the fluctuations or ripple in the flow out of the discharge accumulator through the return channel may be reduced to that shown in curve (e) of FIG. 9.

Referring more particularly to FIG. 8, there is shown another impact tool having a housing 300. A sleeve 302 in the housing 300 together with insert sleeves 304 and 306, which are provided for ease of assembly, define a bore 308 in which a piston 310 may oscillate in a direction along the axis of the bore. A shank 312, for which a rotation mechanism, similar to that shown in FIG. 1, may be provided, presents an impact surface 314 for the lower end 316 of the piston 310. The piston 310 thus acts as a hammer for providing percussive forces upon impact with the shank 312. The shank may be connected to a drill steel and a bit for drilling holes in a formation, say for construction, quarrying or mining purposes.

The piston 310 has a central section 320 which is of greater diameter than the diameter of the lower section 322 as well as the diameter of an upper section 324 of the piston 310. The lower section 322 has a larger diameter than the upper section 324, such that opposite faces 326 and 328 of the center sec-tion 320 respectively present a larger area and a smaller area to a first cavity 330 and a second cavity 332, the end boundaries of which are defined by the faces 326 and 328. While these faces 326 and 328 are shown in the form of steps, other boundary surfaces of other shape may be provided, the term face being used to define any such boundary surface in general. The first cavity 330 provides a drive cavity for the piston and includes the valve mechanism for switching the fluid pressure from supply to return therein, while the second cavity 332 is exposed to the supply pressure at all times.

A valve mechanism 334, consisting of a supply port 336, a return port 338, a valve element 340, and spaced rings 342 and 344 on the piston 310 which engage the valve element 340, is located in drive cavity 330. The ports 336 and 338 are provided by peripheral grooves which extend cicumferentially around the inner wall of the bore 308 as in a manner similar to that shown in FIG. 3B. The opposite edges of the valve element 340 provide porting edges which afford full peripheral porting to which efficiency advantages mentioned above are attendant. The valve element is slidably mounted within the bore 308 coaxial to the piston 310 and has channels 346 which extend longitudinally thereof as was described in connection with the valve element 122 (FIG. 1).

The second cavity 332 as well as the supply port 336 are in communication by way of lateral channels 348 and 350 with a circumferential gallery 352 which extends therebetween. This gallery 352 is also in communication with a supply accumulator 354 by way of a large lateral opening 356 and a multiplicity of channels 358 in the wall of the accumulator 354 which is adjacent to the opening 356. The accumulator 354 may be of a design similar to the accumulator 54 (FIG. 1

Another gallery encompasses the upper end of the drive cavity 330 and is in communication with the return port 338 via a lateral channel 362. The gallery 360 is connected by way of a large opening 364 to a return accumulator 366. A multiplicity of channels 368 in the wall of the accumulator 366 adjacent the opening 364 provides direct communication between the return accumulator 366 and the gallery 360. The return accumulator 366 may be similar to the return accumulator 56 (FIG. 1). The return of the supply of pressurized hydraulic fluid is connected by way of a channel 370 to the return gallery 360. A similar channel 371 into the lateral opening 356 provides for connection of the supply for the source of pressurized fluid to the supply gallery 352.

U-cups and O-ring seals, respectively for sliding surfaces and stationary surfaces are shown to seal the cavities and fluid channels in the housing. Cleansing fluid, such as compressed air, may be communicated through the piston 310 and the shank 312 by way of a pipe 372 which extends through bores therein, as was described in connection with FIG. 1.

The description of operation of the impact tool shown in FIG. 8, will be aided by reference being also made to FIG. 10. FIG. 8 depicts the position of the piston 310 and the valve element 340 just at the instant of impact with the shank (viz., when the piston reaches the impact position). The length of the valve 340 with respect to the return and supply ports 338 and 336, and the position of the ring 342 on piston 310 is such that the return port 338 will immediately become opened and the supply port 336 closed as the valve element 340 travels downward somewhat from the position shown in FIG. 8. Then, during the first portion of the cycle of oscillation, from T to T, (see FIG. 10 (a) pressurized fluid is applied to the second cavity 332 but the drive cavity 330 is open to return by the valve mechanism. The ratio of the areas of the faces 326 to 328 is preferably of the order of 2:1. The pressurized fluid acting on theface 328 drives the piston upwardly in a direction away from the impact position.

When the lower ring 344 on piston 310 raises the valve element 340 to the position shown in FIG. 8, switching occurs in the drive cavity. Pressurized fluid is then applied by way of the gallery 352 to both the second and drive cavities. The net force on the piston 310 has now reversed and is in a direction toward the shank. The return port 338 is closed. The initial momentum of the piston 310 enables it to be carried upward to the limit of its displacement Xp (See FIG. 10 (a)). Net flow is into the accumulator 354. At the top of its stroke at time T the kinetic energy of the piston is stored in the accumulator 354 as well as in the fluid in the cavities and galleries and channels associated therewith. The piston 310 is then driven downwardly during the period T to Tp and over the entire displacement Xp to the impact position. Then the valve mechanism is activated and the return port 338 is opened and the supply port 336 is closed causing the cycle to repeat. The energy stored in the accumulator is transferred during the period T to Tp into percussive forces which are transmitted to the shank 312 and via the shank to the drill steel and bit for rock drilling or other purposes.

The characteristics of the massive piston, the springlike fluid in the cavities, galleries and channels as well as the accumulator, define a relaxation oscillator which develops percussive forces especially adapted for timedependent loads such as are encountered in rock drilling.

As shown in FIG. (b), the flow into the drive cavity 330 is cut off during the initial portion of the cycle from T to T Then flow during the second part of the cycle from T to T is outward from the drive cavity as the kinetic energy of the hammer is stored in the fluid, springs, and accumulator 354. The displacement of fluid into the second cavity 332 increases from T to T and then decreases (outward from the cavity) during the remainder of the cycle from T to T The flow from the second cavity is communicated with the gallery 352 and, when combined with the flow to the first cavity, tends to reduce the net dynamic flow requirements from the accumulator. The net dynamic flow from the accumulator 354 is illustrated in curve (c) of FIG. 10. It will be seen from this curve that the net flow fluctuations are reduced from those associated with the first or drive cavity.

The flow fluctuations to the return accumulator 366 as seen by the return channel 370 exists only during the first portion of the cycle from T to T as shown in FIG. 10 (d) since thereafter the return port is closed. It will be seen, therefore, that the fluctuations in the return path of the configuration of FIG. 8 are generally reduced relative to those present in the configuration of FIG. 1. In particular, the discharge fluctuations of FIG. 10 (d) compared with those of FIG. 9 (d), are seen to be only half as large.

As will be seen, reduced discharge fluctuations can also be provided for in the configuration of FIG. 1 by means of an auxiliary return cavity illustrated as cavity 170 (FIG. 11) and discussed in connection with FIG. 9 (e).

Referring to FIG. 11, there is shown an impact tool having a hammer 130 movable in a bore within a housing 132. The housing has also mounted thereon a supply accumulator l40 and a return accumulator 142. The supply line 144 from the source of pressurized hydraulic fluid (e.g., a hydraulic pump) enters into the supply accumulator 140. A return line 146 enters the return or discharge accumulator 142.

A small diameter step 148 and a large diameter step 150 on the piston 130, which provide faces forming the differential area, also partially bound the second cavity 152 and the first cavity 154, respectively, in the housing 132. A gallery 156 communicates the second and first cavities 152 and 154 when the supply port 158 is opened by the valve element 160. The valve element 160 also switches the fluid pressure in the first cavity 154 from supply pressure to return pressure by closing the supply port 158 and opening the return port 162. The impact tool as shown in FIG. 11 thus operates like the tool shown in FIG. 1, and the supply pressure fluctuation is minimized by virtue of the interconnection of the first and second cavities, as was explained in connection with FIGS. 1 through 8.

In order to minimize the fluctuations in the discharge flow, the impact tool shown in FIG. 11 is equipped with a lower piston section 164, which with the piston section 166 adjacent thereto forms a step 168. The piston section 164 has the same area as the section of the piston providing the step 150. This step 168 bounds one end of a lower cavity 170 which varies in volume, as the piston moves, in a sense opposite to the variation in volume of the first cavity 154. Accordingly, the pressurized fluid can flow back and forth between the first cavity and the cavity 170 by way of a gallery 174 which provides communication therebetween. The discharge accumulator also opens into the gallery 174 by way of an unrestricted passage 176.

When the discharge port 162 is open the volume flow through the discharge port caused by the motion of the face presented by the step is equal, but opposite in sign, to the volume flow due to the piston step 168. The discharge accumulator 142 therefore does not see any net volume displacement. It is only when the discharge port 162 is closed that the discharge accumulator sees a volume displacement. This is during the interval T to T when the piston 130 is being accelerated in the upward direction away from the impact load. During the interval T to T volume displacement into the discharge accumulator 142 is provided by the lower cavity due to the movement of the step 168. This volume displacement in the discharge accumulator as seen by the return channel 146 is shown in curve (e) of FIG. 9. The discharge pulsation is thus reduced to approximately one-half the fluctuation shown in curve (d) of FIG. 9 which depicts the case illustrated in FIG. 1 where a lower cavity is not used.

Referring to FIG. 12, a housing is provided with a bore 182 in which the hammer of the tool, provided by a piston 184, oscillates. A supply accumulator 186 and a return accumulator 188 are shown located on opposite sides of the housing 180. While such location provides a more balanced size and weight relation which may be desired in some applications for impact tools, other accumulator locations may be used. The tool has a first caviity 190 and a second cavity 192. The first cavity performs the same function as the first cavity 94 of FIG. 1 while the second cavity 192 performs the same function as the cavity 96 of FIG. 1, however their positions are reversed. Such reversal provides the feature of simplification of the construction of the piston 184. The piston may be a two-part structure consisting of a lower part 194, the upper end of which 196 is threaded. The upper part 198 of the piston is in the form of an internally threaded disc having an axially extending rim 200. The entire part 198 may be screwed onto the threaded end 196 in a manner of a nut. A valve element 202, can, by virtue of the 2-part construction of the piston 184, be assembled on the piston in the first cavity 190. The same 2-part construction feature can be implemented in connection with the configuration shown in the other FIGS. of the drawing, including FIGS. 1 and 8.

The valve element 202 in FIG. 12 is provided with a centrally disposed lip 204 which is engaged between the rim 200 and a shoulder 206 of the piston 184. The rim 200 and shoulder 206 are spaced longitudinally from each other a distance, relative to the length of the lip 204 of the valve 202 to provide the desired delay displacement and free stroke X,, of the valve 202. The valve element 202 is also vented by way of holes 208 which extend longitudinally therethrough. A number of such holes, which perform the same function as the groove 90 in the valve element 122 (FIG. 1) are distributed around the valve element 202.

The second cavity 192 isconnected to the first cavity 190 by way of a channel 210. The supply line 212 also 192 when the return or discharge port 218 is opened and the supply port 216 is closed. Accordingly, the fluctuations are minimized and maintenance of constant pressure aided as was explained in connection with FIG. 1. The discharge port 218 is connected to the discharge accumulator 188 via an opening 219. The return line 220 also enters into this opening. The discharge fluctuations-are similar to those depicted in FIG. 9 (d).

The impact tool shown in FIG. 13 is similar to that tool shown in FIG. 12, like parts being identified with like reference numerals. An additional cavity 230 is partially bounded by a piston step 232 of the same area as the piston step 234 which defines and varies the volume of the first cavity 190. The step 234 has a larger area than the step 236 which defines and varies the volume of the second cavity 192.

To provide for the volume-flow back and forth be tween the additional cavity 230 and the drive cavity 190, a channel 240 is provided which extends longitudinally between the discharge port 218 and the additional cavity 230. The return accumulator also is connected to the channel 240 by way of an opening 242. The return line 220 also enters the channel. It'will therefore be observed that the flow fluctuations in the impact tool shown in FIG. 13 are minimized, both as regards the supply and the return flows.

Referring to FIG. 14, there is shown an impact tool which is similar, insofar as the construction of its piston 184 is concerned, with the tool shown in FIG. 12 and like parts of these tools identified with like referenced numerals. The valve element 202 is provided with a peripheral slot 250 which is centrally located between the upper and lower ends of the valve element 202. The slot communicates with the vents 208. The porting between the supply and return ports 216 and 218 is therefore through the slot 250. The efiective length of the valve element 208 is therefore the width (in the vertical direction) of the slot 250.

The supply port 216 is now located below the return port 218. This permits the channel 210 (FIG. 12) to be provided by a gallery 252 which extends circumferentially around the housing and encircles the piston 184. The use of this gallery simplifies the construction of the housing and assures unrestricted communication between the first cavity 190 and the-second cavity 192.

From the foregoing description it will be apparent that there has been provided improved impact tools which generate percussive energy. While various embodiments of the tools which incorporate the invention have been described for purposes of illustration, variations and modifications therein the scope of the invention will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken as illustrative and not in any limiting sense.

What is claimed is:

l. A hydroacoustic oscillator operated by a pressurized fluid source having a supply and a return, said oscillator comprising a mass movable in one direction and then in the opposite direction during each cycle of its oscillation,

means including said mass defining at least a first cavity and a second cavity, the volume of which are varied by said mass in opposite senses with movement of said mass in the same direction,

means providing a third cavity, said third cavity being a gallery extending along the path of movement of said mass between said first and second cavities and being in communication with said second cavity, said gallery being disposed circumferentially around said first and second cavities,

means for maintaining said supply in communication with one of said second cavity and said third cavity for maintaining said pressurized fluid in said second cavity for the entire cycle of oscillation of said mass,

said mass presenting in a plane normal to the motion of said mass a larger area to said first cavity than to said second cavity,

means operated by said mass for providing communication between said first cavity and said supply and said first cavity and return during successive portions of each cycle of oscillation, and

means also providing communication between said first and third cavities during that portion of each cycle when said first cavity is in communication with said supply whereby to provide a direct path for flow exchange through said third cavity between-said first and second cavities due to the motion of said mass and the difference in said areas presented by said mass to said first and second cavities.

2. The invention as set forth in claim 1 including a fourth cavity, said mass operated means providing communication between said fourth cavity and said first cavity only during that portion of each said cycles when communication between said first cavity and said return is provided, said fourth cavity also being in communication with said return.

3. The invention as set forth in claim 1 including means coupled to said third cavity for reducing the stiffness presented by said fluid therein, and in said second cavity and also in said first cavity during that portion of each of said cycles when communication between said first and third cavities is provided by said mass operated means.

4. The invention as set forth in claim 3 wherein said stiffness reducing means is an accumulator.

5. The invention as set forth in claim 2 including accumulator means communicating with said fourth cavity.

6. The invention as set forth in claim 1 wherein said means including said mass also defines a fourth cavity and wherein said mass operated means is operative to provide communication between said fourth cavity and said first cavity during that portion of the cycle when it provides communication of said first cavity with said return.

7. The invention as set forth in claim 6 wherein said fourth cavity is a gallery disposed circumferentially around said first cavity and is spaced from said third cavity.

8. The invention as set forth in claim 7 including supply and return accumulators spaced laterally from said third and fourth cavities, separate channels extending respectively from said supply accumulator to said third cavity and from said return accumulator to said fourth cavity.

9. A hydroacoustic oscillator operated by a pressurized fluid source having a supply and a return, said oscillator comprising a mass movable in one direction and then in the opposite direction during each cycle of its oscillation,

means including said mass defining at least a first cavity and a second cavity, the volume of which are varied by said mass in opposite senses with movement of said mass in the same direction,

means providing a third cavity in communication with said second cavity, means for maintaining said supply in communication with one of said second cavity and said third cavity for maintaining said pressurized fluid in said second cavity for the entire cycle of oscillation of said mass,

said mass presenting in a plane normal to the motion of said mass a larger area to said first cavity than to said second cavity,

means operated by said mass for providing communication between said first cavity and said supply and said first cavity and return during successive portions of each cycle of oscillation, means also providing communication between said first and third cavities during that portion of each cycle when said first cavity is in communication with said supply whereby to provide a direct path for flow exchange through said third cavity between said first and second cavities due to the motion of said mass and the difference in said areas presented by said mass to said first and second cavities, and

said mass operated means comprising a valve mechanism including a port structure having first and second ports respectively communicating said supply and said return with said first cavity for the supply and discharge of said fluid therefrom, and a valve element in said first cavity bi-directionally movable by said mass for opening said first port and closing said second port as said element moves with said mass for one of said successive portions of each cycle of oscillation and then for closing said first port and opening said second port for the other of said successive portions of said cycle to abruptly switch pressure in said first cavity between supply and return valves, said first port being in communication with said third cavity.

10. The invention as set forth in claim 9 wherein said mass is generally cylindrical, said first cavity and said second cavity are also generally cylindrical and are spaced from each other along the axis of said mass, said ports include circumferential grooves extending around the outer periphery of said first cavity, and said element is a generally cylindrical member coaxial with respect to said outer periphery and axially movable in said first cavity by said mass over said grooves.

11. The invention as set forth in claim 10 wherein said third cavity includes a generally cylindrical chamber coaxial with said mass and spaced laterally therefrom and porting means providing an essentially unrestricted passage extending laterally between said second cavity and said third cavity.

12. The invention as set forth in claim 9 wherein said valve element extends longitudinally along the periphery of said first cavity a distance at least equal to the distance from the end of said first port to the end of said second port, said element also having passages therein providing communication between the portions of said first cavity adjacent to the opposite ends of said element.

13. The invention as set forth in claim 12 wherein said element has at least one opening disposed between said first and second ports for alternatively communicating said first and second ports with said first cavity when said element moves certain distances longitudinally in a direction toward said first port and toward said second port, respectively.

14. An impact tool for applying percussive forces to a load which comprises a. a housing having a bore therein,

b. a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses with movement of said piston in either of said directions, said first face having a larger area than said second face,

pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with pressurized fluid which exerts force on said second face to move said piston in one of said directions,

(1. a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means, said valve mechanism including first and second ports communicating with said first cavity and a valve element movable by said piston for opening said first port and closing said second port during a portion of the cycle of oscillation of said piston and for closing said first port and opening said second port during the remainder of said cycle,

e. an accumulator providing fluid energy storage means, and

f. means communicating said accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means including a gallery extending circumferentially around said bore and spaced laterally therefrom and extending longitudinally between said first port and said second cavity and common to said first port, said second cavity and said accumulator, said communicating means providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means.

15. The invention as set forth in claim 14 wherein said fluid is a hydraulic fluid and said accumulator is a body having a cavity having first and second regions separated by a flexible diaphragm, said first region being open to said communicating means and said sec ond region being precharged with a compressible fluid.

16. The invention as set forth in claim 14 including a second accumulator in communication with said return and also with said first cavity when said valve mechanism communicates said return with said first cavity.

17. The invention as set forth in claim 14 including a second accumulator, a second gallery around said bore and spaced laterally therefrom, and said second gallery communicating with said second port and said second accumulator.

18. The invention as set forth in claim 17 wherein said piston has successive longitudinally spaced sec tions of first, second and third diameters, said second diameter being larger than said first diameter and said third diameter being smaller than said first diameter to define said first and second faces on opposed sides of the second diameter piston section.

19. The invention as set forth in claim 18 wherein said piston has a fourth section of diameter equal to the diameter of said second section, said third section being disposed between said second and fourth sections, said fourth section defining a third face opposed to said second face, said third face defining a third cavity encircling a portion of said third section adjacent to said third face, a second gallery also encircling said third section and spaced laterally from said third cavity, said second gallery extending longitudinally between said second port and said third cavity and being in communication therewith and with said second accumulator.

20. An impact tool for applying percussive forces to a load which comprises (a) a housing having a bore therein,

(b) a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses with movement of said piston in either of said directions, said first face having a larger area than said second face,

(c) pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with pressurized fluid which exerts force on said second face to move said piston in one of said directions,

(d) a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means,

(e) a first accumulator providing fluid energy storage means,

(f) means communicating said first accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means also providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means,

g. a second accumulator in communication with said return and also with said first cavity when said valve mechanism communicates said return with said first cavity, and

b. said piston having a third face having an area equal to the area of said first face and defining a third cavity in said bore, the volume of which third cavity increases and decreases in the sense opposite to the increase and decrease of the volume of said first cavity, and a channel common to said second accumulator, said third cavity and said first cavity when said valve mechanism communicates said first cavity with said return.

21. An impact tool for applying percussive forces to a load which comprises a. a housing having a bore therein,

b. a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses with movement of said piston in either of said directions, said first face having a larger area than said second face,

pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with pressurized fluid which exerts force on said second face to move said piston in one of said directions,

d. a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means, said valve mechanism including first and second ports communicating with said first cavity and a valve element movable by said piston for opening said first port and closing said second port during a portion of the cycle of oscillation of said piston and for closing said first port and opening said second port during the remainder of said cycle,

e. an accumulator providing fluid energy storage means, and

f. means communicating said accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means,

g. said piston having first and second sections separated by a third section of diameter smaller than said first and second sections, said first and third sections forming a step therebetween which defines said first face and said third and second sections forming a step therebetween which defines said second face, said first and second faces being opposed to each other and separated by a portion of said housing extending to said third section to define said first and second cavities, a second accumulator communicating with said second port and said return.

22. The invention as set forth in claim 21 wherein said piston has a first part including said third section and said second section, said third section having an external thread on the end thereof opposite to the end thereof adjacent to said second section, said first section being internally threaded and being assembled to said first named end of said third section.

23. The invention as set forth in claim 22 wherein said first section has a rim and said third section has a step located in opposed relation in said first cavity, said valve element having a lip extending laterally toward said third section and disposed longitudinally between said rim and said third section step for movement of said element by said piston in opposite directions when said lip is engaged by said rim and said step respectively.

24. The invention as set forth in claim 21 wherein said piston has a fourth section of diameter smaller than said first section and forming a step which is disposed on the side of said first section opposite to said third section, said last named step defining a third face having an area equal to the area of said first face, said third face defining a third cavity in said housing which encircles said fourth section, a channel extending longitudinally between said second port and said third cavity and communicating therewith and with said second accumulator.

25. The invention as set forth in claim 21 wherein said second cavity is disposed closer than said first cavity to the end of said housing adapted to be disposed adjacent said load, said first port being disposed closer than said first port to said second cavity, a gallery in said housing spaced laterally outward of said cavities, said gallery extending longitudinally between said first port and said second cavity and communicating therewith and with said first accumulator, said valve element being a sleeve encircling said third section and having a lip extended laterally inward to a location between opposed steps longitudinally spaced from each other and extending laterally outward to alternatively engage said lip as said piston oscillates in opposite directions, said sleeve being longitudinally vented and having a central groove in its outer peripheral surface extending to the vent, said groove being narrower longitudinally than the distance between said first and second ports, and said sleeve being longer than the distance separating the edges of said ports spaced furthest apart from each other. 

1. A hydroacoustic oscillator operated by a pressurized fluid source having a supply and a return, said oscillator comprising a mass movable in one direction and then in the opposite direction during each cycle of its oscillation, means including said mass defining at least a first cavity and a second cavity, the volume of which are varied by said mass in opposite senses with movement of said mass in the same direction, means providing a third cavity, said third cavity being a gallery extending along the path of movement of said mass between said first and second cavities and being in communication with said second cavity, said gallery being disposed circumferentially around said first and second cavities, means for maintaining said supply in communication with one of said second cavity and said third cavity for maintaining said pressurized fluid in said second cavity for the entire cycle of oscillation of said mass, said mass presenting in a plane normal to the motion of said mass a larger area to said first cavity than to said second cavity, means operated by said mass for providing communication between said first cavity and said supply and said first cavity and return during successive portions of each cycle of oscillation, and means also providing communication between said first and third cavities during that portion of each cycle when said first cavity is in communication with said supply whereby to provide a direct path for flow exchange through said third cavity between said first and second cavities due to the motion of said mass and the difference in said areas presented by said mass to said first and second cavities.
 2. The invention as set forth in claim 1 including a fourth cavity, said mass operated means providing communication between said fourth cavity and said first cavity only during that portion of each said cycles when communication between said first cavity and said return is provided, said fourth cavity also being in communication with said return.
 3. The invention as set forth in claim 1 including means coupled to said third cavity for reducing the stiffness presented by said fluid therein, and in said second cavity and also in said first cavity during that portion of each of said cycles when communication between said first and third cavities is provided by said mass operated means.
 4. The invention as set forth in claim 3 wherein said stiffness reducing means is an accumulator.
 5. The invention as set forth in claim 2 including accumulator means communicating with said fourth cavity.
 6. The invention as set forth in claim 1 wherein said means including said mass also defines a fourth cavity and wherein said mass operated means is operative to provide communication between said fourth cavity and said first cavity during that portion of the cycle when it provides communication of said first cavity with said return.
 7. The invention as set forth in claim 6 wherein said fourth cavity is a gallery disposed circumferentially around said first cavity and is spaced from said third cavity.
 8. The invention as set forth in claim 7 including supply and return accumulators spaced laterally from said third and fourth cavities, separate channels extending respectively from said supply accumulator to said third cavity and from said return accumulator to said fourth cavity.
 9. A hydroacoustic oscillator operated by a pressurized fluid source having a supply and a return, said oscillator comprising a mass movable in one direction and then in the opposite direction during each cycle of its oscillation, means including said mass defining at least a first cavity and a second cavity, the volume of which are varied by said mass in opposite senses with movement of said mass in the same direction, means providing a third cavity in communication with said second cavity, means for maintaining said supply in communication with one of said second cavity and said third cavity for maintaining said pressurized fluid in said second cavity for the entire cycle of oscillation of said mass, said mass presenting in a plane normal to the motion of said mass a larger area to said first cavity than to said second cavity, means operated by said mass for providing communication between said first cavity and said supply and said first cavity and return during successive portions of each cycle of oscillation, means also providing communication between said first and third cavities during that portion of each cycle when said first cavity is in communication with said supply whereby to provide a direct path for flow exchange through said third cavity between said first and second cavities due to the motion of said mass and the difference in said areas presented by said mass to said first and second cavities, and said mass operated means comprising a valve mechanism including a port structure having first and second ports respectively communicating said supply and said return with said first cavity for the supply and discharge of said fluid therefrom, and a valve element in said first cavity bi-directionally movable by said mass for opening said first port and closing said second port as said element moves with said mass for one of said successive portions of each cycle of oscillation and then for closing said first port and opening said second port for the other of said successive portions of said cycle to abruptly switch pressure in said first cavity between supply and return valves, said first port being in communication with said third cavity.
 10. The invention as set forth in claim 9 wherein said mass is generally cylindrical, said first cavity and said second cavity are also generally cylindrical and are spaced from each other along the axis of said mass, said ports include circumferential grooves extending around the outer periphery of said first cavity, and said element is a generally cylindrical member coaxial with respect to said outer periphery and axially movable in said first cavity by said mass over said grooves.
 11. The invention as set forth in claim 10 wherein said third cavity includes a generally cylindrical chamber coaxial with said mass and spaced laterally therefrom and porting means providing an essentially unrestricted passage extending laterally between said second cavity and said third cavity.
 12. The invention as set forth in claim 9 wherein said valve element extends longitudinally along the periphery of said first cavity a distance at least equal to the distance from the end of said first port to the end of said second port, said element also having passages therein providing communication between the portions of said first cavity adjacent to the opposite ends of said element.
 13. The invention as set forth in claim 12 wherein said element has at least one opening disposed between said first and second ports for alternatively communicating said first and second ports with said first cavity when said element moves certain distances longitudinally in a direction toward said first port and toward said second port, respectively.
 14. An impact tool for applying percussive forces to a load which comprises a. a housing having a bore therein, b. a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses with movement of said piston in either of said directions, said first face having a larger area than said second face, c. pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with presSurized fluid which exerts force on said second face to move said piston in one of said directions, d. a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means, said valve mechanism including first and second ports communicating with said first cavity and a valve element movable by said piston for opening said first port and closing said second port during a portion of the cycle of oscillation of said piston and for closing said first port and opening said second port during the remainder of said cycle, e. an accumulator providing fluid energy storage means, and f. means communicating said accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means including a gallery extending circumferentially around said bore and spaced laterally therefrom and extending longitudinally between said first port and said second cavity and common to said first port, said second cavity and said accumulator, said communicating means providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means.
 15. The invention as set forth in claim 14 wherein said fluid is a hydraulic fluid and said accumulator is a body having a cavity having first and second regions separated by a flexible diaphragm, said first region being open to said communicating means and said second region being precharged with a compressible fluid.
 16. The invention as set forth in claim 14 including a second accumulator in communication with said return and also with said first cavity when said valve mechanism communicates said return with said first cavity.
 17. The invention as set forth in claim 14 including a second accumulator, a second gallery around said bore and spaced laterally therefrom, and said second gallery communicating with said second port and said second accumulator.
 18. The invention as set forth in claim 17 wherein said piston has successive longitudinally spaced sections of first, second and third diameters, said second diameter being larger than said first diameter and said third diameter being smaller than said first diameter to define said first and second faces on opposed sides of the second diameter piston section.
 19. The invention as set forth in claim 18 wherein said piston has a fourth section of diameter equal to the diameter of said second section, said third section being disposed between said second and fourth sections, said fourth section defining a third face opposed to said second face, said third face defining a third cavity encircling a portion of said third section adjacent to said third face, a second gallery also encircling said third section and spaced laterally from said third cavity, said second gallery extending longitudinally between said second port and said third cavity and being in communication therewith and with said second accumulator.
 20. An impact tool for applying percussive forces to a load which comprises (a) a housing having a bore therein, (b) a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses wIth movement of said piston in either of said directions, said first face having a larger area than said second face, (c) pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with pressurized fluid which exerts force on said second face to move said piston in one of said directions, (d) a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means, (e) a first accumulator providing fluid energy storage means, (f) means communicating said first accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means also providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means, g. a second accumulator in communication with said return and also with said first cavity when said valve mechanism communicates said return with said first cavity, and h. said piston having a third face having an area equal to the area of said first face and defining a third cavity in said bore, the volume of which third cavity increases and decreases in the sense opposite to the increase and decrease of the volume of said first cavity, and a channel common to said second accumulator, said third cavity and said first cavity when said valve mechanism communicates said first cavity with said return.
 21. An impact tool for applying percussive forces to a load which comprises a. a housing having a bore therein, b. a piston mounted in said bore for oscillatory movement in opposite directions toward and away from said load and having first and second faces which respectively define end boundaries to first and second cavities in said bore, the volumes of said first and second cavities changing in opposite senses with movement of said piston in either of said directions, said first face having a larger area than said second face, c. pressurized hydraulic fluid supply and return means in said housing, said second cavity communicating with said supply means for filling said second cavity with pressurized fluid which exerts force on said second face to move said piston in one of said directions, d. a valve mechanism contained in said first cavity and movable by said piston for alternatively communicating said first cavity with said supply and return means for applying forces to said first face of said piston in the other of said opposite directions when said first cavity is in communication with said supply means, said valve mechanism including first and second ports communicating with said first cavity and a valve element movable by said piston for opening said first port and closing said second port during a portion of the cycle of oscillation of said piston and for closing said first port and opening said second port during the remainder of said cycle, e. an accumulator providing fluid energy storage means, and f. means communicating said accumulator with said second cavity, with said supply means and also with said first cavity, when said valve mechanism communicates said supply with said first cavity, and for storing energy in said storage means when said piston is moving away from said load, thereby to bring said piston movement to a stop, said energy being returned to said piston as said piston accelerates back in the direction toward said load for applying said percussive forces thereto, said communicating means providing unrestricted passage for the exchange of fluid between said first and second cavities for reducing fluctuations in flow with respect to said storage means, g. said piston having first and second sections separated by a third section of diameter smaller than said first and second sections, said first and third sections forming a step therebetween which defines said first face and said third and second sections forming a step therebetween which defines said second face, said first and second faces being opposed to each other and separated by a portion of said housing extending to said third section to define said first and second cavities, a second accumulator communicating with said second port and said return.
 22. The invention as set forth in claim 21 wherein said piston has a first part including said third section and said second section, said third section having an external thread on the end thereof opposite to the end thereof adjacent to said second section, said first section being internally threaded and being assembled to said first named end of said third section.
 23. The invention as set forth in claim 22 wherein said first section has a rim and said third section has a step located in opposed relation in said first cavity, said valve element having a lip extending laterally toward said third section and disposed longitudinally between said rim and said third section step for movement of said element by said piston in opposite directions when said lip is engaged by said rim and said step respectively.
 24. The invention as set forth in claim 21 wherein said piston has a fourth section of diameter smaller than said first section and forming a step which is disposed on the side of said first section opposite to said third section, said last named step defining a third face having an area equal to the area of said first face, said third face defining a third cavity in said housing which encircles said fourth section, a channel extending longitudinally between said second port and said third cavity and communicating therewith and with said second accumulator.
 25. The invention as set forth in claim 21 wherein said second cavity is disposed closer than said first cavity to the end of said housing adapted to be disposed adjacent said load, said first port being disposed closer than said first port to said second cavity, a gallery in said housing spaced laterally outward of said cavities, said gallery extending longitudinally between said first port and said second cavity and communicating therewith and with said first accumulator, said valve element being a sleeve encircling said third section and having a lip extended laterally inward to a location between opposed steps longitudinally spaced from each other and extending laterally outward to alternatively engage said lip as said piston oscillates in opposite directions, said sleeve being longitudinally vented and having a central groove in its outer peripheral surface extending to the vent, said groove being narrower longitudinally than the distance between said first and second ports, and said sleeve being longer than the distance separating the edges of said ports spaced furthest apart from each other. 